Open since March, a small structure in the Hudson River Park at Spring St., the New Runners Shack is helping put a spring in joggers steps. A nonprofit partnership of Nike and the Hudson River Park Trust, the shack, which is, naturally, staffed by runners, offers Powerbars, water and Powergels for $1. (Powergels are not for hair sculpting on the windy Hudson, but an easily dissolvable energy formula to be sucked down when one is hitting the wall.) Gatorade is $1.50. Free are bandages, hair ties, Vaseline, small lockers and dog biscuits. The Runners Shack has no large, visible Nike logos, though there was a small one on the visor of one of the shacks attendants last Sunday. The shacks most popular function is to hand out a map to runners showing mileage distances in the park. During the short time The Villager stopped by last weekend to check the place out, two runners came up asking for information on mileage and were given a map and a quick rundown on the distances. The shack has also proven popular with dogs, some of whom cant pass by without a return visit for another biscuit. All of the shacks proceeds go to the Trust.